Fixes for vacuum_cleanup_index_scale_factor GUC option

vacuum_cleanup_index_scale_factor was located in autovacuum group of
GUCs.  However, it affects not only autovacuum, but also manually run
VACUUM.  It appears that "client connection defaults" group of GUCs
is more appropriate for vacuum_cleanup_index_scale_factor, because
vacuum_*_age options are already located there.

Also, vacuum_cleanup_index_scale_factor was missed in
postgresql.conf.sample.  So, add it there with appropriate comment.

Author: Masahiko Sawada with minor editorization by me
Discussion: https://postgr.es/m/CAD21AoArsoXMLKudXSKN679FRzs6oubEchM53bHwn8Tp%3D2boNg%40mail.gmail.com

doc/src/sgml/config.sgml

@@ -1882,50 +1882,6 @@ include_dir 'conf.d'
      </note>
     </sect2>
 
-    <sect2 id="runtime-config-index-vacuum">
-     <title>Index Vacuum</title>
-     <variablelist>
-     <varlistentry id="guc-vacuum-cleanup-index-scale-factor" xreflabel="vacuum_cleanup_index_scale_factor">
-      <term><varname>vacuum_cleanup_index_scale_factor</varname> (<type>floating point</type>)
-      <indexterm>
-       <primary><varname>vacuum_cleanup_index_scale_factor</varname> configuration parameter</primary>
-      </indexterm>
-      </term>
-      <listitem>
-       <para>
-        Specifies the fraction of the total number of heap tuples counted in
-        the previous statistics collection that can be inserted without
-        incurring an index scan at the <command>VACUUM</command> cleanup stage.
-        This setting currently applies to B-tree indexes only.
-       </para>
-
-       <para>
-        If no tuples were deleted from the heap, B-tree indexes are still
-        scanned at the <command>VACUUM</command> cleanup stage when at least one
-        of the following conditions is met: the index statistics are stale, or
-        the index contains deleted pages that can be recycled during cleanup.
-        Index statistics are considered to be stale if the number of newly
-        inserted tuples exceeds the <varname>vacuum_cleanup_index_scale_factor</varname>
-        fraction of the total number of heap tuples detected by the previous
-        statistics collection. The total number of heap tuples is stored in
-        the index meta-page. Note that the meta-page does not include this data
-        until <command>VACUUM</command> finds no dead tuples, so B-tree index
-        scan at the cleanup stage can only be skipped if the second and
-        subsequent <command>VACUUM</command> cycles detect no dead tuples.
-       </para>
-
-       <para>
-        The value can range from <literal>0</literal> to <literal>100</literal>.
-        When <varname>vacuum_cleanup_index_scale_factor</varname> is set to
-        <literal>0</literal>, index scans are never skipped during
-        <command>VACUUM</command> cleanup. The default value is <literal>0.1</literal>.
-       </para>
-
-      </listitem>
-     </varlistentry>
-     </variablelist>
-    </sect2>
-
     <sect2 id="runtime-config-resource-background-writer">
      <title>Background Writer</title>
 
@@ -7003,6 +6959,45 @@ COPY postgres_log FROM '/full/path/to/logfile.csv' WITH csv;
       </listitem>
      </varlistentry>
 
+     <varlistentry id="guc-vacuum-cleanup-index-scale-factor" xreflabel="vacuum_cleanup_index_scale_factor">
+      <term><varname>vacuum_cleanup_index_scale_factor</varname> (<type>floating point</type>)
+      <indexterm>
+       <primary><varname>vacuum_cleanup_index_scale_factor</varname> configuration parameter</primary>
+      </indexterm>
+      </term>
+      <listitem>
+       <para>
+        Specifies the fraction of the total number of heap tuples counted in
+        the previous statistics collection that can be inserted without
+        incurring an index scan at the <command>VACUUM</command> cleanup stage.
+        This setting currently applies to B-tree indexes only.
+       </para>
+
+       <para>
+        If no tuples were deleted from the heap, B-tree indexes are still
+        scanned at the <command>VACUUM</command> cleanup stage when at least one
+        of the following conditions is met: the index statistics are stale, or
+        the index contains deleted pages that can be recycled during cleanup.
+        Index statistics are considered to be stale if the number of newly
+        inserted tuples exceeds the <varname>vacuum_cleanup_index_scale_factor</varname>
+        fraction of the total number of heap tuples detected by the previous
+        statistics collection. The total number of heap tuples is stored in
+        the index meta-page. Note that the meta-page does not include this data
+        until <command>VACUUM</command> finds no dead tuples, so B-tree index
+        scan at the cleanup stage can only be skipped if the second and
+        subsequent <command>VACUUM</command> cycles detect no dead tuples.
+       </para>
+
+       <para>
+        The value can range from <literal>0</literal> to <literal>100</literal>.
+        When <varname>vacuum_cleanup_index_scale_factor</varname> is set to
+        <literal>0</literal>, index scans are never skipped during
+        <command>VACUUM</command> cleanup. The default value is <literal>0.1</literal>.
+       </para>
+
+      </listitem>
+     </varlistentry>
+
      <varlistentry id="guc-bytea-output" xreflabel="bytea_output">
       <term><varname>bytea_output</varname> (<type>enum</type>)
       <indexterm>

src/backend/utils/misc/guc.c

@@ -3248,7 +3248,7 @@ static struct config_real ConfigureNamesReal[] =
 	},
 
 	{
-		{"vacuum_cleanup_index_scale_factor", PGC_USERSET, AUTOVACUUM,
+		{"vacuum_cleanup_index_scale_factor", PGC_USERSET, CLIENT_CONN_STATEMENT,
 			gettext_noop("Number of tuple inserts prior to index cleanup as a fraction of reltuples."),
 			NULL
 		},

src/backend/utils/misc/postgresql.conf.sample

@@ -575,6 +575,9 @@
 #vacuum_freeze_table_age = 150000000
 #vacuum_multixact_freeze_min_age = 5000000
 #vacuum_multixact_freeze_table_age = 150000000
+#vacuum_cleanup_index_scale_factor = 0.1	# fraction of total number of tuples
+						# before index cleanup, 0 always performs
+						# index cleanup
 #bytea_output = 'hex'			# hex, escape
 #xmlbinary = 'base64'
 #xmloption = 'content'